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Suppose you have an iterable items containing items that should be put in a queue q. Of course you can do it like this:

for i in items:
    q.put(i)

But it feels unnecessary to write this in two lines - is that supposed to be pythonic? Is there no way to do something more readable - i.e. like this

q.put(*items)
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  • 1
    The asterisk syntax is by some considered to be magic. The for-loop makes it clear to most people what is going on. Commented Aug 13, 2015 at 12:07
  • @StefanvandenAkker my very late answer to that argument: I suppose readability is very subjective - so shame on me for this type of question I guess. But with that said: the concept of packing/unpacking arguments with the asterisk has been part of python since - i believe the mid-2000's or so - and other languages have it as well. Even JavaScript had adopted the concept back then in 2015 with its spread operator - so I would argue that it isn't that unpopular. Commented Mar 4, 2021 at 20:12

3 Answers 3

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16

Using the built-in map function :

map(q.put, items)

It will apply q.put to all your items in your list. Useful one-liner.

For Python 3, you can use it as following :

list(map(q.put, items))

Or also :

from collections import deque
deque(map(q.put, items))

But at this point, the for loop is quite more readable.

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6 Comments

While I like that better a little bit, I don't think its really nice - it would be nicer in haskell, but thats just my taste. but the main problem is: this only works for python 2.x
@IARI, you could also do [q.put(i) for i in items]. But as I indicated in my answer, I would just use the code you have in your question.
Edited for python 3 support.
Thanks - if find myself doing that a lot (composing list with map). But i think it's rather noisy and this defeats the purpose of readability a bit. Same with the list comprehension - I don't think its really readable. Both options seem to be a bit of an abuse.
Comprehensions and map are intended for when you want the result, not as a way to have one-liner for loops; besides, in this case, you could just do for i in items: q.put(i).
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What's unreadable about that?

for i in items:
    q.put(i)

Readability is not the same as "short", and a one-liner is not necessarily more readable; quite often it's the opposite.

If you want to have a q.put(*items)-like API, consider making a short helper function, or subclassing Queue.

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6 Comments

while you're absolutely right that short is not the same as readable, I would think if one does know python a bit q.put(*items) would be more readable, wouldn't you agree? in the end shorter is always more readable, if what the abbreviation does is clear to the literate reader.
@IARI, there's nothing wrong with that necessarily, though in the case of Queue.put, it wouldn't always make sense to be able to put more than one item at a time, due to blocking and timeouts. But if you wanted to write a helper function to do it for you (e.g. put_items(q, *items); or in a subclass of Queue, q.put_items(*items)), I wouldn't have any objections to that. You could even call it put, as you said. Notice that I did mention both options in my answer :).
I guess I was partially responding to your question, and partially to FunkySayu's suggestion of map(q.put, items).
right, I think the blocking is a better answer. I still feel a bit patronized as in "We're not letting you put iterables in queues because you might forget about blocking" ... But probably that is the main reason why the standart api doesn't have any way to do it, right?
@IARI, I don't know if that's why, but it's a good reason, especially when it's extremely trivial to do it yourself if you need to, as opposed to making the API even a little bit harder to use (or easier to misuse, as the case may be).
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-3 
q.extend(items)

Should be simple and Pythonic Enough

If you want it at the front of the queue

q.extendleft(items)

Python Docs:

https://docs.python.org/2/library/collections.html#collections.deque.extend

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Queue class doesn't have extend method

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